The genetic stability and metabolic robustness of production strains is one of the key criteria for the production of bio-based products by microbial fermentation on an industrial scale. These criteria were here explored in an industrial ethanol-producer strain of Saccharomyces cerevisiae able to co-ferment D-xylose and L-arabinose with glucose through the chromosomal integration of several copies of pivotal genes for the use of these pentose (C5) sugars. Using batch sequential cultures in a controlled bioreactor that mimics long-term fermentation in an industrial setting, this strain was found to exhibit significant fluctuations in D-xylose and L-arabinose consumption as early as the 50th generation and beyond. These fluctuations seem not related to the few low-consumption C5 sugar clones that appeared throughout the sequential batch cultures at a frequency lower than 1.5% and that were due to the reduction in the number of copies of transgenes coding for C5 sugar assimilation enzymes. Also, subpopulations enriched with low or high RAD52 expression, whose expression level was reported to be proportional to homologous recombination rate did not exhibit defect in C5-sugar assimilation, arguing that other mechanisms may be responsible for copy number variation of transgenes. Overall, this work highlighted the existence of genetic and metabolic instabilities in an industrial yeast which, although modest in our conditions, could be more deleterious in harsher industrial conditions, leading to reduced production performance.

中文翻译：

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用于 C5 糖利用的工业酿酒酵母菌株长期发酵过程中的基因组和代谢不稳定性

生产菌株的遗传稳定性和代谢稳健性是工业规模微生物发酵生产生物基产品的关键标准之一。这些标准是在工业乙醇生产菌株中进行探索的酿酒酵母通过几个关键基因拷贝的染色体整合，能够将 D-木糖和 L-阿拉伯糖与葡萄糖共同发酵，以利用这些戊糖 (C5)。在模拟工业环境中长期发酵的受控生物反应器中使用分批连续培养，发现该菌株早在第 50 代及以后就表现出 D-木糖和 L-阿拉伯糖消耗的显着波动。这些波动似乎与整个连续批次培养中出现频率低于 1.5% 的少数低消耗 C5 糖克隆无关，这是由于编码 C5 糖同化酶的转基因拷贝数减少所致。此外，亚群富含低或高RAD52据报道，其表达水平与同源重组率成正比，但 C5 糖同化并没有表现出缺陷，认为其他机制可能是转基因拷贝数变异的原因。总体而言，这项工作强调了工业酵母中存在遗传和代谢不稳定性，尽管在我们的条件下是适度的，但在更恶劣的工业条件下可能更有害，导致生产性能下降。